Prolonged epicardial mapping of myocardial infarction: The effects of propranolol and intra-aortic balloon pumping following coronary artery occlusion

An electrocardiographic model of myocardial ischemic injury

Previous electrocardiographic models of myocardial ischemic injury have assumed that transmembrane potential changes are uniform throughout a region of ischemia such that injury currents arise exclusively at the boundary between normal and ischemic myocardium. In such models, the distribution and amplitude of ST segment deflections are considered to arise from a polarized surface interfacing normal and ischemic myocardium. This concept in modeling ischemic injury was derived from the application of principles of electric field theory which had been successfully applied previously to ventricular activation in which QRS potentials are considered to arise from polarized surfaces representing the relatively narrow interfaces between depolarized and nondepolarized myocardium. The present paper outlines the limitations of modeling ischemic injury as a polarized surface in terms of the failure of the predictions of such a model to be supported by the experimentally observed: 1) distribution and relative amplitude of epicardial ST segment elevation overlying a region of ischemia; 2) directional changes in epicardial ST segment elevation that occur with changes in the size of an ischemic region; and 3) nonuniform distribution of transmembrane potential changes which occur within a region of ischemia. A new electrocardiographic model of ischemic injury is formulated which accounts for the nonuniform distribution of transmembrane potential changes which occur throughout a region of ischemia. The model accurately describes experimental observations regarding ST segment deflections which had remained inconsistent with previous models.

Low-dose propranolol for the protection of the left ventricle from ischaemic damage

Global myocardial ischaemia improves intracardiac operating conditions but damages the myocardium. Propranolol should reduce this damage but may impair postoperative myocardial contractility. An assessment of its protective effect during 90 minutes of normothermic ischaemia in canine hearts has been made. The early and late changes of contractility caused by low-dose propranolol were also recorded. A comparison of cardiac isovolumic contractile force, velocity, and compliance was made in three groups of dogs given 30 microgram/kg of propranolol with or without 90 minutes of cardiac ischaemia, or cardiac ischaemia without propranolol. Contractile force and velocity were significantly reduced by the propranolol, but recovered fully after 90 minutes. Ischaemia without propranolol reduced force and velocity of contraction significantly more than ischaemia with propranolol. Propranolol thus reduces operative ischaemic damage without itself impairing postoperative function.